Implantable Stimulator With a Conformable Foil-Like Electrode Array

ABSTRACT

An implantable stimulator is provided having a conformable foil-like substrate, having a longitudinal axis extending from a pulse generator to a distal end of the substrate. The substrate comprising one or more adjacent polymeric substrate layers and an electrode array. The electrode array having a first and second electrode where one or more electrical interconnections are comprised in the substrate. The conformable foil-like substrate has a maximum thickness of 0.5 millimeter or less, proximate the electrodes. By providing a more easily patternable multilayer substrate, more complicated electrode array configurations may be supported, allowing a higher degree of flexibility to address transverse and/or longitudinal misalignment. By providing a relatively thin implantable electrode array user comfort may be increased through application of energy to tissue by the implantable stimulator.

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BACKGROUND

Implantable electrical stimulation systems may be used to deliverelectrical stimulation therapy to patients to treat a variety ofsymptoms or conditions such as headaches, lower back pain andincontinence.

In many electrical stimulation applications, it is desirable for astimulator, typically comprising a therapeutic lead (a lead compriseselectrodes and electrical connections), to provide electricalstimulation to one or more precise locations within a body—in manycases, precisely aligning the stimulation electrodes during implantationmay be difficult due to the curvature of tissues and anatomicalstructures. A mismatch in curvature of the electrode section of a leadmay create unexpected and/or unpredictable electrical resistance betweenone or more electrodes and the underlying tissue. In addition, repeatedmovement of the relevant areas of the body may even worsen the mismatch.A particular problem with subcutaneous implants is that even smalldifferences in flexibility between the implant and surrounding tissuemay affect patient comfort, and can cause irritation of the overlyingskin. This is a particular problem with sub-cutaneous implants.

More recently, use has been made of plastics and polymers, which have aninherent flexibility or may be made in a curved shape—for example, asdescribed in US application US 2016/0166828. Although such leads may bemanufactured in a curved-shape or deformed by human manual manipulationduring implantation, this is inconvenient. The high degree of anatomicvariability found in humans and animals means that a manufacturer mustprovide either a large range or pre-curved leads or allow the leads tobe made to measure. In the case that they are deformable duringimplantation, this further complicates the implantation process.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain illustrative embodiments illustrating organization and method ofoperation, together with objects and advantages may be best understoodby reference to the detailed description that follows taken inconjunction with the accompanying drawings in which:

FIG. 1A is a transverse view of a first implementation of an implantablestimulator consistent with certain embodiments of the present invention.

FIG. 1B is a top view of a first implementation of an implantablestimulator consistent with certain embodiments of the present invention.

FIG. 1C is a bottom view of a first implementation of an implantablestimulator consistent with certain embodiments of the present invention.

FIG. 2A is a transverse view of a second implementation of animplantable stimulator consistent with certain embodiments of thepresent invention.

FIG. 2B is a top view of a second implementation of an implantablestimulator consistent with certain embodiments of the present invention.

FIG. 2C is a bottom view of a second implementation of an implantablestimulator consistent with certain embodiments of the present invention.

FIG. 3A is a transverse view of a third implementation of an implantablestimulator consistent with certain embodiments of the present invention.

FIG. 3B is a top view of a third implementation of an implantablestimulator consistent with certain embodiments of the present invention.

FIG. 3C is a bottom view of a third implementation of an implantablestimulator consistent with certain embodiments of the present invention.

FIG. 4A is a first view of alternative electrode configurations of animplantable stimulator consistent with certain embodiments of thepresent invention.

FIG. 4B is a second view of alternative electrode configurations of animplantable stimulator consistent with certain embodiments of thepresent invention.

FIG. 4C is a third view of alternative electrode configurations of animplantable stimulator consistent with certain embodiments of thepresent invention.

FIG. 5 presents locations of nerves in the anterior portion of a humanhead that may be treated through operation of an implantable stimulatorconsistent with certain embodiments of the present invention.

FIG. 6 presents locations of nerves in the posterior portion of a humanbody that may be treated through operation of an implantable stimulatorconsistent with certain embodiments of the present invention.

FIG. 7 presents locations of nerves in a human body that may be treatedthrough operation of an implantable stimulator consistent with certainembodiments of the present invention.

DETAILED DESCRIPTION

While this invention is susceptible of embodiment in many differentforms, there is shown in the drawings and will herein be described indetail specific embodiments, with the understanding that the presentdisclosure of such embodiments is to be considered as an example of theprinciples and not intended to limit the invention to the specificembodiments shown and described. In the description below, likereference numerals are used to describe the same, similar orcorresponding parts in the several views of the drawings.

The terms “a” or “an”, as used herein, are defined as one or more thanone. The term “plurality”, as used herein, is defined as two or morethan two. The term “another”, as used herein, is defined as at least asecond or more. The terms “including” and/or “having”, as used herein,are defined as comprising (i.e., open language). The term “coupled”, asused herein, is defined as connected, although not necessarily directly,and not necessarily mechanically.

Reference throughout this document to “one embodiment”, “certainembodiments”, “an embodiment” or similar terms means that a particularfeature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment of the presentinvention. Thus, the appearances of such phrases or in various placesthroughout this specification are not necessarily all referring to thesame embodiment. Furthermore, the particular features, structures, orcharacteristics may be combined in any suitable manner in one or moreembodiments without limitation.

In the following detailed description, numerous non-limiting specificdetails are given to assist in understanding this disclosure.

FIGS. 1A, 1B & 1C depict longitudinal cross-sections through a firstembodiment 100 of an implantable stimulator comprising:

-   -   a pulse generator 500 (only depicted in FIGS. 1B and 1C) for        generating one or more electrical treatment stimulation pulses;        and    -   a conformable foil-like substrate 300 having a longitudinal axis        600 extending from the pulse generator 500 to a distal end of        the substrate 300. The substrate 300 comprises one or more        adjacent polymeric substrate layers and has a first 310 and        second 320 planar surface.

The implantable stimulator 100 also comprises:

-   -   an electrode array 200, 400, proximate the distal end, having        one or more electrodes of a first 200 a, 200 b type and one or        more electrodes of a second type 400 a, 400 b. The electrodes        200, 400 are comprised in the first 310 or second 320 surface,        and each is configurable for transferring treatment energy, in        use, to (as a stimulation electrode) and/or from (as a return        electrode) human or animal tissue. In this context, an array may        be considered a systematic arrangement of two or more electrodes        200 a, 200 b, 400 a, 400 b. 1D, 2D or 3D arrays may be provided.        Optionally, they may be arranged in rows and/or columns.

The implantable stimulator 100 further comprises:

-   -   one or more electrical interconnections 250, between the pulse        generator 500 and the first 200 a, 200 b and the second 400 a,        400 b electrodes, for transferring electrical energy as one or        more electrical treatment stimulation pulses to the first        electrode 200 a, 200 b and/or the second electrodes 400 a, 400        b. The one or more electrical interconnections 250 are comprised        between the first surface 310 and the second 320 surfaces.

In this disclosure, the conformability of the electrode array 200, 400is determined to a high degree by the one or more of the following:

-   -   the conformability of the substrate 300 proximate the electrodes        200, 300;    -   the arrangement and positions of the electrodes 200, 400;    -   the materials and dimensions (or extent) of the materials        comprised in the electrodes 200, 400;    -   the arrangement and positions of the one or more        interconnections 250 proximate the electrodes 200, 400; and    -   the materials and dimensions (or extent) of the materials        comprised in the interconnections 200, 400.

By suitable configuration, arrangement and optimization, an implantableelectrode array 200, 400 may be provided which is foil-like (orfilm-like) and highly conformable.

As depicted, the conformable foil-like substrate 300 is preferablyelongated along the longitudinal axis 600, having a tape-like shape,allowing the pulse generator 500 to be disposed further away from theposition of the electrodes 200, 400.

If the substrate 300 is substantially planar (in a non-limiting example,by allowing the substrate 300 to conform to a planar surface), the first310 and second 320 surfaces are disposed along substantially paralleltransverse planes 600, 700. As depicted in FIG. 1A, the first surface310 lies in a plane comprising the longitudinal axis 600 and a firsttransverse axis 700—the first transverse axis 700 is substantiallyperpendicular to the longitudinal axis 600. As depicted in FIG. 1A, theplane of the first surface 310 is substantially perpendicular to theplane of the cross-section drawing (substantially perpendicular to thesurface of the paper).

The conformable foil-like substrate 300 has a maximum thickness of 0.5millimeter or less, proximate the first 200 a, 200 b and second 400 a,400 b electrodes, the thickness being determined by a perpendiculardistance between corresponding points on the first 310 and second planarsurfaces 320. This is preferably determined when the substrate 300conforms to a planar surface.

The foil-like substrate 300 has a thickness or extent along a secondtransverse axis 750—this second transverse axis 750 is substantiallyperpendicular to both the longitudinal axis 600 and the first transverseaxis 700—it lies in the plane of the drawing (along the surface of thepaper) as depicted. The first surface 310 is depicted as an uppersurface and the second surface 320 is depicted as a lower surface.

The thickness may therefore be determined by a perpendicular distancealong the second transverse axis 750 between corresponding points on thefirst 310 and second planar surfaces 320. The maximum thickness of theconformable foil-like substrate 300 proximate the first 200 a, 200 b andsecond 400 a, 400 b electrodes is 0.5 mm or less, preferably 0.3millimeters or less, even more preferably 0.2 millimeters or less, yetmore preferably 0.1 millimeters or less.

In general, the lower the maximum thickness (in other words, the thinnerthe substrate), the higher the degree of conformance.

To clarify the differences between the different views depicted, theaxes are given nominal directions:

-   -   the longitudinal axis 600 extends from the proximal end (not        depicted in FIG. 1A, but depicted in FIGS. 1B and 1C) on the        left, to the distal end, depicted on the right of the page;    -   the first transverse axis 700 extends into the page as depicted;        and    -   the second transverse axis 750 extends from bottom to top as        depicted.

The conformable foil-like substrate 300 may be described as amultilayer—it comprises one or more adjacent polymeric substrate layershaving the first 310 and second 320 planar surface. The one or moreelectrical interconnections 250 are also comprised between the first 310and second 320 planar surfaces. However, it is not necessary that theone or more polymeric layers and/or interconnections have similarextents along the first transverse axis 700. In other words, within thecontext of this disclosure, there may be regions where aninterconnection 250 is sandwiched between regions of polymeric substrate(appears as a multilayer in a longitudinal cross-section), adjacent toregions where the polymeric substrate is substantially contiguous.Similarly, there may be regions where an interconnection 250 issandwiched between two polymeric substrate layers (appears as amultilayer in a longitudinal cross-section), adjacent to regions wherethe substrate comprises two adjacent substrate layers. Similarly, asubstrate comprising two or more polymeric substrate layer may bemodified (physically and/or chemically), such that it appears to be onelayer of polymeric substrate.

These polymeric substrate layers are selected for suitability to beconformable, and to comprises the one or more electricalinterconnections 250. Preferably, the polymeric substrate materials arealso biocompatible and durable, such as a material selected from thegroup comprising silicone rubber, siloxane polymers,polydimethylsiloxanes, polyurethane, polyether urethane,polyetherurethane urea, polyesterurethane, polyamide, polycarbonate,polyester, polypropylene, polyethylene, polystyrene, polyvinyl chloride,polytetrafluoroethylene, polysulfone, cellulose acetate,polymethylmethacrylate, polyethylene, and polyvinylacetate. Suitablepolymer materials, including LCP (Liquid Crystal Polymer) films, aredescribed in “Polymers for Neural Implants”, Hassler, Boretius,Stieglitz, Journal of Polymer Science: Part B Polymer Physics, 2011, 49,18-33 (DOI 10.1002/polb.22169), In particular, Table 1 is included hereas reference, depicting the properties of Polyimide (UBE U-Varnish-S),Parylene C (PCS Parylene C), PDMS (NuSil MED-1000), SU-8 (MicroChem SU-82000 & 3000 Series), and LCP (Vectra MT1300).

Conformable foil-like substrates 300 are configured to follow thecontours of the underlying anatomical features very closely by beingflexible. Very thin foil-like substrates 300 have the additionaladvantage that they have increased flexibility.

Most preferably, the polymeric substrate layers comprise an LCP,Parylene and/or a Polyimide. LCP's are chemically and biologicallystable thermoplastic polymers which allow for hermetic sensor moduleshaving a small size and low moisture penetration.

Advantageously, an LCP may be thermoformed allowing complex shapes to beprovided. Very thin (and subsequently very conformable) and very flat(highly planar) layers of an LCP may be provided. For fine tuning ofshapes, a suitable laser may also be used for cutting.

In a non-limiting example, a conformable foil-like substrate 300 of LCPmay have a thickness (extent along the second transverse axis 750) inthe range 50 microns (um) to 720 microns (um), preferably 100 microns(um) to 300 microns (um). In an exemplary embodiment, values of 150 um(micron), 100 um, 50 um, or 25 um may be provided. When conforming to asubstantially planar surface, the foil-like surface 300 is substantiallycomprised in a plane with a transverse extent substantiallyperpendicular to the longitudinal axis 600, wherein the planar width maybe determined by a perpendicular distance between corresponding pointson outer surfaces edges of the planar foil-like substrate 300 along thetransverse extent. As depicted, this is along the first transverse axis700. In an embodiment, Electrode 200, 400 widths of 2 mm to 20 mm may beprovided using LCP.

At room temperature, thin LCP films have mechanical properties similarto steel. This is important as implantable substrates 300 must be strongenough to be implanted, strong enough to be removed (explanted) andstrong enough to follow any movement of the neighboring anatomicalfeatures and/or structures without deteriorating.

LCP belongs to the polymer materials with the lowest permeability forgases and water. LCP's can be bonded to themselves, allowing multilayerconstructions with a homogenous structure.

In contrast to LCP's, polyimides are thermoset polymers, which requireadhesives for the construction of multilayer electrode arrays.Polyimides are thermoset polymer material with high temperature andflexural endurance.

In an embodiment, an LCP may be used to provide conformable substrate300 as a—in other words, two or more adjacent polymeric substratelayers. In a non-limiting example, these may be layers of 25 um (micron)thickness.

In an embodiment, one or more electrical interconnections 250 may beprovided between the first (310) and second (320) surfaces bymetallization. These may be conductors embedded in the substrate 300such as having a single polymer layer and applying conductive materialusing suitable deposition techniques known from the semiconductorindustry.

In an embodiment, if more than one adjacent polymeric substrate layer isprovided, an interconnection layer may be provided using suitabletechniques such as those from the semiconductor industry. The polymericsubstrate layers may also be considered adjacent when one of moreadhesion layers are used between them.

In an embodiment, lamination may also be used to provide a substrate 300with the desired physical and chemical properties, and/or to provide aconvenient method of manufacture. In a non-limiting example, a substrate300 may comprise three laminated polymer layers: two high temperaturethermoplastic layers with a low-temperature layer (bond-ply) in between,and high-temperature layers towards the first surface 310 and secondsurface 320.

In an alternative embodiment, two layers of silicone may be provided aspolymeric substrate layers: one layer of silicone is provided, metal ispatterned on one of its outer surfaces, and a second layer of siliconeis added over the metal patterning by jetting, over-molding, orspin-coating.

In an embodiment, the electrical interconnections 250 may comprise oneor more conductive materials, such as a metal, formed as required in oneor more conductive elements: wire, strand, foil, lamina, plate, and/orsheet. They may be a substantially contiguous (one conductor). They mayalso comprise more than one conductor, configured and arranged to be, inuse, electrically connected with each other—in other words, the one ormore conductors are configured and arranged to be substantiallyelectrically contiguous in use.

Alternatively, the one or more electrical interconnections 250 may becomprised in one or more conductive interconnection layers 250, the oneor more conductive interconnection layers being comprised between twoadjacent polymeric substrate layers. As depicted in FIG. 1A, a pluralityof interconnections may be provided at different dispositions (ordepths) between the first surface 310 and the second surface 320.

In an embodiment, an interconnection 250 in the context of thisdisclosure is not configured or arranged to be, in use, in contact withhuman or animal tissue. The one or more interconnections 250 areembedded in one or more layers of a low conductance or insulatingpolymer, such as LCP. Additionally or alternatively, one or moreencapsulation layers may be used.

One or more interconnection layers 250 may also be provided bymetallization using techniques from the PCB (Printed Circuit Board)industry, such as metallization with a bio-compatible metal such as goldor platinum. Electro-plating may be used. Layers comprising LCP filmsare particularly suitable for metallization. These electricalinterconnections 250 and/or interconnect layers 250 are configured totransfer electrical energy as one or more electrical treatmentstimulation pulses from the pulse generator 500 to the first electrode200 a, 200 b and/or the second electrodes 400 a, 400 b.

Using suitable polymeric substrate materials, such as an LCP film,allows the conformable foil-like (or film-like) substrate 300 andelectrode array 200, 300 to have a high width-to-height ration,providing a bio-compatible electronic foil (or film), or bio-electronicfoil (or film).

In an embodiment, when the substrate 300 conforms to a substantiallyplanar surface, the ratio of maximum planar width to maximum thicknessproximate the first 200 a, 200 b and second 400 a, 400 b electrodes maybe 7:1 or higher, preferably 10:1 or higher, more preferably 15:1 orhigher, yet more preferably 30:1 or higher, even more preferably 50:1 orhigher.

Ratios of 100:1 or higher may also be advantageous, and may be providedusing one or more mechanically strong substrate layers of an LCP film,with a width of approximately 20 mm and a thickness of approximately 0.2mm. This provides a high degree of flexibility, and therefore also ahigh degree of conformability. Additional measures may also be taken toincrease the degree of conformability in the first transverse direction700, such as varying the width of the substrate, adding one or moreundulations and/or providing bending points.

In a non-limiting example, when using a single row of electrodes 200,400 and/or electrodes 200, 400 with a smaller width, the width may befour mm with a thickness of approximately 0.2 mm—this is a ratio ofapproximately 20:1.

In a non-limiting example, proximate the pulse generator 500, greaterextents may be required which further depend, to a high degree, on thedimensions of the electronic components used a width of twenty mm and athickness of three mm. This is a ratio of approximately 6.67:1.

As depicted in FIG. 1A, the distal end of the conformable foil-likesubstrate 300 comprises:

-   -   two electrodes 200 a, 200 b of a first type, comprised in the        first surface 310, and    -   two electrodes 400 a, 400 b of a second type, also comprised in        the first surface 310. From proximal to distal end, the order        depicted is 200 a, 400 a, 200 b, 400 b—in other words, each        electrode of the first type 200 a, 200 b is proximate an        electrode of the second type 400 a, 400 b and comprised in the        same surface 310.

The foil-like substrate 300 comprises an electrical interconnection 250between each electrode 200 a, 400 a, 200 b, 400 b and the pulsegenerator. In this embodiment, each electrical interconnection 250 isconfigured and arranged such that each electrode 200 a, 400 a, 200 b,400 b is electrically connected substantiallyindependently—consequently, one of the operating modes available bysuitably configuring the pulse generator 500 is substantiallyindependent operation. The pulse generator 500 may be configured usingone or more hardware, firmware and/or software parameters.

Although depicted in FIG. 1A as individual connections 250 at differentdistances between the first 310 and second 320 surfaces, the skilledperson will also realize that the same interconnections may be providedby a suitably configured interconnections 250 (or an interconnectionlayer 250) at approximately the same distance between the first 310 andsecond 320 surfaces, similar to the embodiment depicted in FIG. 3B, anddescribed below.

“Comprised in” the first 310 or second 320 surface means that theelectrodes 200 a, 400 a, 200 b, 400 b are relatively thin (such as whenthe substrate conforms to a substantially planar surface, having anextent along the second transverse axis of 20 to 50 microns or less.Thinner electrodes may be also be used to further increase the degree ofconformability, such as 1 micron or less), and attached to (or at leastpartially embedded in) the surface.

The electrodes 200 may comprise a conductive material such as gold,platinum, platinum black, TiN, IrO₂, iridium, and/or platinum/iridiumalloys and/or oxides. Conductive polymers, such as Pedot, may also beused. Preferably, bio-compatible conductive materials are used.PCB/metallization techniques may be used to attach them to the first 310and/or second 330 surfaces of the one or more polymeric substratelayers.

Thicker metal layers are generally preferred over thinner metal layersfor electrodes 200 a, 200 b, 400 a, 400 b because they can be subjectedto bodily substances that may dissolve the metal. However, thicker metallayers typically increase rigidity (reduce conformability) proximate thethicker layer.

The stimulator 100 may be implanted by first creating a subcutaneoustunnel and/or using an implantation tool. However, the high degree ofconformability may make successful implantation more difficult. Evenwhen using a suitable insertion tool, the electrode positions may befound later to be incorrect due to misalignment, lead migration duringimplantation, or lead migration after transplantation.

At least the distal end comprising the electrode array 200, 400, isimplanted. However, it may be advantageous to implant the stimulator100.

In addition, during implantation, it may be difficult to preciselyidentify the desired position for the stimulation. When implanted thestimulator electrodes should be positioned sufficiently close to thenerve to be stimulated. But nerve pathways may not always be clearlyvisible to the professional performing the implantation, and thedisposition and path of the nerve pathways vary greatly fromperson-to-person.

As depicted in FIG. 1, there is no substantial hardware differencebetween the first-type 200 a, 200 b and second type 400 a, 400 belectrodes—any difference in functionality is determined in thisimplementation mainly by the configuration (one or more hardware,firmware and/or software parameters) of the pulse generator 500. Theremay be a smaller influence on the electrical properties due to thearrangement and routing of the interconnections 250.

One or more electrodes of the same type 200 a, 200 b or 400 a, 400 b maybe operated substantially the same by suitable configuration of thepulse generator 500—in other words, the stimulation energy applied tothe electrodes 200, 400 is substantially the same at substantially thesame time instance (usually measured as a voltage, a current, a power, acharge, or any combination thereof). This may also be used to anticipateand/or correct for a misalignment and/or lead migration—this isadvantageous as it allows the configuration to be performed at leastpartially using software.

Additionally or alternatively, two or more electrodes 200, 400 may beconfigured and arranged using one or more parameters of the pulsegenerator 500 as a stimulation electrode or a return electrode. This mayprovide a higher degree of configurability as it only becomes necessaryto implant the substrate 300 such that at least two of the electrodesare proximate the desired stimulation location.

In this embodiment 100, the electrodes of the first type 200 a, 200 bare nominally configured and arranged to be operated as a stimulationelectrode.

The electrodes of the second type 400 a, 400 b are nominally configuredto be operated as a return electrode—each is configured to provide, inuse, an electrical return for one or more stimulation electrode 200 a,200 b. In other words, the electrical return 400 a, 400 b closes theelectrical circuit. It may also be similarly configured to provide anelectrical ground for a corresponding electrical energy source.

Three configurations are thus provided based on this nominalconfiguration: either:

-   -   a stimulation/return electrode pair 200 a/400 a proximate the        first surface 310 at that stimulation/return location; or    -   a stimulation/return electrode pair 200 b/400 b proximate the        first surface 310 at that stimulation/return location; or    -   a combination thereof.

In an embodiment, one or more stimulation electrodes 200 a, 200 b may beprovided in such a stimulator 100. The number, dimensions and/orspacings of the stimulating electrodes 200 a, 200 b may be selected andoptimized depending on the treatment. In an embodiment, if more than onestimulation electrode 200 a, 200 b is provided, each stimulationelectrode 200 a, 200 b may provide:

-   -   a different stimulation effect, a similar stimulation effect or        the same stimulation effect.

To avoid a misalignment, a selection may be made of one or twoelectrodes 200 a, 200 b proximate the tissues where the effect is to becreated.

Two or more stimulation electrodes 200 a, 200 b may be made active atsubstantially the same time if stimulation over a larger area isrequired and/or at a location between the active stimulation electrodes200 a, 200 b.

In an embodiment, a stimulation electrode 200 a, 200 b may havedimensions in the order of six to eight mm along the longitudinal axis600, and three to five mm along the first transverse axis 700, soapproximately 18 to 40 square mm (mm²).

A foil-like substrate 300, suitable for an implant, may comprise up totwelve stimulation 200 a, 200 b and return 400 a, 400 b electrodes overa length of 15 cm to allow for a correction for misalignment, or tosimply allow the healthcare professional to select the most effectivestimulation location.

In an embodiment, FIG. 1B depicts a view of the second surface 320 ofthe implantable distal end of the foil-like substrate 300 depicted inFIG. 1A. In other words, the second surface 320 is depicted in the planeof the paper, lying along the longitudinal axis 600 (depicted frombottom to top) and in the first transverse axis 700 (depicted from leftto right). The second transverse axis 750 extends into the page. Thefirst surface 310 is not depicted in FIG. 1B, but lies at a higherposition along the second transverse axis 750 (into the page), and isalso substantially parallel to the plane of the drawing. The foil-likesubstrate 300 conforms to a substantially planar surface.

The pulse generator 500 may be disposed between the second 320 surfaceand the first 310 surface. In FIGS. 1B and 1C, it is depicted withdotted lines. Alternatively, the pulse generator 500 may be at leastpartially disposed on the first surface 310 or on the second surface320. Alternatively, the pulse generator 500 may be at least partiallyembedded in the first surface 310 or in the second surface 320.

Depending on the degree of embedding and the one or more electricalcomponents used for the pulse generator 500, the maximum thickness maybe optimized. Components may be thinned to minimize the thickness. Byusing a conformable foil-like substrate 300 as disclosed herein, themaximum thickness of the implantable stimulator 100 proximate the pulsegenerator 500 may be five millimeters or less, preferably fourmillimeters or less, even more preferably three millimeters or less, thethickness being determined by a perpendicular distance betweencorresponding points on outer planar surfaces when the implantablestimulator 100 conforms to a substantially planar surface. Additionaloptional electrical components, such as an antenna, comprising a coil ordipole or fractal antenna, may also influence the thickness depending onthe degree that they are embedded in the substrate.

The stimulator 100 and the foil-like substrate 300 extend along thefirst transverse axis 700 (considered the planar width of the stimulator100/foil-like substrate 300 when conforming to a substantially planarsurface). As depicted, the planar width proximate the pulse generator500 may be greater than the planar width proximate the electrodes 200 a,200 b, 400 a, 400 b at the distal end of the foil-like substrate 300.The planar width proximate the pulse generator 500 may depend on thehardware and components used for the pulse generator 500—typically, itis at least the width of the integrated circuit used for the pulsegenerator 500. Additional optional electrical components, such as anantenna comprising a coil or dipole or fractal antenna, may alsoinfluence the planar width.

In an embodiment, the planar width proximate the electrodes 200 a, 200b, 400 a, 400 b may depend on the conductors used for the electrodes 200a, 200 b, 400 a, 400 b and the one or more interconnections 250. In anembodiment, the planar width is at least the width of the firstelectrode 200 a, 200 b or the second electrode 400 a, 400 b.

In an embodiment, FIG. 1C depicts a view of the first surface 310 of theimplantable distal end of the foil-like substrate 300 depicted in FIGS.1A and 1B. In other words, the first surface 310 is depicted in theplane of the paper, lying along the longitudinal axis 600 (depicted frombottom to top) and in the first transverse axis 700 (depicted from rightto left). The second transverse axis 750 extends out of the page. Thisis the view facing the animal or human tissue which is stimulated (inuse). The second surface 320 is not depicted in FIG. 1C, but lies at alower position along the second transverse axis 750 (into the page), andis also substantially parallel to the plane of the drawing. Thefoil-like substrate 300 conforms to a substantially planar surface.

The one or more interconnections 250 are disposed between the first 310surface and the second 320 surface, as depicted in FIG. 1A. In FIG. 1C,they are depicted as dotted lines, representing the interconnections 250(or suitably configured one or more interconnection layers 250) thathave been provided for each of the electrodes 200 a, 200 b, 400 a, 400 bin this embodiment. A single dotted line 250 is depicted between thepulse generator 500 and the electrodes 200, 400 to indicate, inembodiment 100, that the interconnections 250 are at approximately thesame disposition along the first transverse axis 700.

As depicted in FIG. 1C, the electrodes 200 a, 200 b, 400 a, 400 b eachhave a longitudinal extent (length) along the longitudinal axis 600 anda transverse extent (width) along the first transverse axis 700.

Although depicted as similar, in practice, each electrode 200 a, 200 b,400 a, 400 b may vary in shape, transverse cross-section, orientationand/or size (or extent), depending on the intended use and/or thedesired degree of configurability.

After implantation of the stimulator 100, or at least of the distal endcomprising the electrode array 200, 400, the pulse generator 500 may beconfigured and arranged to provide, in use, electrical energy to the oneor more electrodes of the first type 200 a, 200 b with respect to theelectrical return applied to the one or more electrode of the secondtype 400 a, 400 b.

The configurability of the stimulator 100 allows, before, during and/orafter implantation of at least of the distal end comprising theelectrode array 200, 400, the operation of the one or more electrodes200 a, 200 b, 400 a, 400 b to be determined and/or adapted. Theoperation may also be reconfigured one or more times during the periodthat the stimulator 100 is implanted to optimize and/or prolongtreatment.

In an embodiment, the pulse generator 500 may be initially configured tonominally operate 200 a and 400 a as respectively a stimulation/returnelectrode pair. After implantation of at least the distal end 200, 400,insufficient stimulation may be observed and/or measured. If it isassumed to be due to a mainly longitudinal misalignment, the pulsegenerator 500 may be alternatively configured, using one or moreparameters, to nominally operate 200 b and 400 b as respectively astimulation/return electrode pair.

The stimulator 100 may be further configured and arranged to switch thepulse generator 500 under predetermined and/or controlled conditionsbetween these configurations. It may be convenient to further considerthese configurations as a first and second electrode modes, and allow auser to select a mode as a preference and/or switch mode. Alternatively,the pulse generator 500 may switch modes under predetermined and/orcontrolled conditions.

Additionally or alternatively, other modes may also be provided forconfiguring the pulse generator 500 to operate in:

-   -   a first electrode mode, wherein electrical stimulation energy is        provided to one or more electrodes of the first type 200 a, 200        b as one or more electrical treatment stimulation pulses, the        one or more electrodes of the second type 400 a, 400 b being        configured to provide, in use, a corresponding electrical return        for the one or more first electrodes 200 a, 200 b; or    -   a second electrode mode, wherein to one or more electrodes of        the second type 400 a, 400 b as one or more electrical treatment        stimulation pulses, the one or more electrodes of the first type        200 a, 200 b being configured to provide, in use, a        corresponding electrical return for the one or more second        electrodes 400 a, 400 b.

Again, the stimulator 100 may be further configured and arranged toswitch the pulse generator 500 under predetermined and/or controlledconditions between these configurations or modes. Additionally oralternatively, a user may be allowed to select a mode as a preferenceand/or switch mode.

The skilled person will realize that the electrodes 200 a, 200 b, 400 a,400 b may be configured to operate in more complex configurations, suchas:

-   -   400 a and 200 a may be operated as respectively a        stimulation/return electrode pair (reversing the original        intended operation);    -   400 b and 200 b may be operated as respectively a        stimulation/return electrode pair;    -   if an intermediate stimulation is preferred, two or more        electrodes 200 a, 200 b, 400 a, 400 b may be operated        substantially simultaneously as one or more stimulation        electrodes;    -   one or more electrodes 200 a, 200 b, 400 a, 400 b may be        operated as one or more return electrodes;    -   electrode 400 a operated as a stimulation electrode, in        combination with electrode 200 a and electrode 200 b as return        electrodes;    -   electrode 400 a and 200 b operated as a stimulation electrode,        in combination with electrode 200 a and electrode 400 b as a        return electrode.

Alternatively or additionally, the shape, orientation, transversecross-section, and/or size (or length) of one or more stimulationelectrodes may be differently configured compared to one or more returnelectrodes.

A number of parameters and properties may be considered when configuringand arranging the foil-like substrate 300 proximate the electrode array200, 400 for conformability, such as:

-   -   the transverse 700 and/or longitudinal extent 600 of the one or        more electrodes 200 a, 200 b, 400 a, 400 b    -   the thickness of the foil-like substrate 300, or the        perpendicular distance between the first surface 310 and the        second surface 320    -   the materials comprised in the foil-like substrate 300, and        their physical properties    -   the number and extent of interconnections 250 and/or        interconnection layers 250 between the first surface 310 and        second surface 320.

There have been attempts to make traditional leads, such as cylindricalleads, much thinner to allow subcutaneous implantation and/or toincrease comfort by flattening. But the surface area of the flattenedelectrodes may become disadvantageously small.

In a non-limiting example, a conventional 0.2 mm round lead with 1 cmlong electrodes is estimated to result in an electrode withapproximately 6 mm² electrode surface.

However, using the conformable electrode arrays described herein, a thinsubstrate 300 with dimensions of 0.2 mm thick, and four mm wide may beconfigured and arranged to provide approximately 35 mm² electrodesurface in the same length. It is estimated that this may reduceimpedance by a factor of approximately 35/6, and reduce powerconsumption by approximately 35/6.

In an embodiment, FIGS. 2A, 2B and 2C depict longitudinal cross-sectionsthrough a second embodiment 101 of an implantable stimulator. It issimilar to the first embodiment 100, depicted in FIGS. 1A, 1B and 1Cexcept:

-   -   instead of four electrodes comprised in the first surface 310,        this embodiment comprises two electrodes in the first surface        310—nominally an electrode of the first type 200 a and nominally        an electrode of the second type 400 a. From proximal to distal        end, the order depicted is 200 a, 400 a—in other words, an        electrode of the first type 200 a is proximate an electrode of        the second type 400 a in the first surface 310.    -   the distal end of the stimulator 101 also comprises two        electrodes in the second surface 320—a further electrode        nominally of the first type 200 b and a further electrode        nominally of the second type 400 b. From proximal to distal end,        the order depicted is 200 b, 400 b—in other words, an electrode        of the first type 200 b is proximate an electrode of the second        type 400 b in the second surface 320.    -   In FIG. 2B, the view of the second surface 320 depicts the two        electrodes 200 a, 400 a comprised in that surface, and one or        more interconnections 250 are depicted using a dotted line;    -   In FIG. 2C, the view of the second surface 320 depicts the two        electrodes 200 b, 400 b comprised in that surface, and one or        more interconnections 250 are depicted using a dotted line;

In this embodiment 101, the electrodes of the first type 200 a, 200 bare nominally configured and arranged to be operated as a stimulationelectrode, and the electrodes of the second type 400 a, 400 b arenominally configured to be operated as a return electrode.

Three main configurations are thus provided:

-   -   a stimulation/return electrode pair 200 a/400 a proximate the        first surface 310; or    -   a stimulation/return electrode pair 200 b/400 b proximate the        second surface 320; or    -   a combination thereof.

This may be advantageous if it is uncertain whether the implantabledistal end of the foil-like substrate 300 may be “above” or “below” thetargeted tissue such as “above” or “below” a nerve. This may bedetermined after implantation by attempting stimulation in each nominalconfiguration and observing and/or measuring the presence of neuralstimulation.

As discussed above, in relation to FIGS. 1A, 1B and 1C, each electrode200 a, 200 b, 400 a, 400 b may be operated as one or more stimulationelectrodes or operated as one or more return electrodes.

In an embodiment, FIGS. 3A, 3B and 3C depict longitudinal cross-sectionsthrough a third embodiment 102 of an implantable stimulator. It issimilar to the second embodiment 101, depicted in FIGS. 2A, 2B and 2Cexcept:

-   -   interconnections 250 are disposed at approximately the same        disposition along the second transverse axis 750, as depicted in        FIG. 3A. The lines 250 are hatched to indicate that they are not        be depicted as being in the same longitudinal        cross-section—there are interconnections 250 disposed at        substantially different positions along the first transverse        axis 700;    -   interconnections 250 are disposed at substantially different        dispositions along the first transverse axis 700, as depicted in        FIGS. 3B and 3C as two adjacent dashed lines between the        electrode array 200, 400 and the pulse generator 500;    -   instead of nominally comprising an electrode of the first 200        and second type 400 in the first surface 310, the first surface        310 comprises a first 200 a and second 200 b electrode nominally        of the first type 200;    -   instead of nominally comprising an electrode of the first 200        and second type 400 in the second surface 320, the second        surface 320 comprises a first 400 a and second 400 b electrode        nominally of the second type 400;

In this embodiment 102, the electrodes of the first type 200 a, 200 bare nominally configured and arranged to be operated as a stimulationelectrode, and the electrodes of the second type 400 a, 400 b arenominally configured to be operated as a return electrode.

Three main configurations are thus provided:

-   -   a stimulation/return electrode pair 200 a/400 a for stimulating        between the first surface 310 and second surface 320 proximate        the location of this electrode pair; or    -   a stimulation/return electrode pair 200 b/400 b for stimulating        between the first surface 310 and second surface 320 proximate        the location of the electrode pair; or    -   a combination thereof.

This may be advantageous to correct for a longitudinal misalignment, orto simply allow the healthcare professional to select the most effectivestimulation location.

As discussed above, in relation to FIGS. 2A, 2B and 2C, each electrode200 a, 200 b, 400 a, 400 b may be operated as one or more stimulationelectrodes or operated as one or more return electrodes.

Additionally or alternatively, one or more electrodes of the same type200 a, 200 b or 400 a, 400 b may be electrically connected to each otherby suitably configuring the one or more interconnections 250. They willthen be operated substantially the same. This may be used to anticipateand/or correct for a misalignment and/or lead migration as longitudinalpositioning is less sensitive (a stimulation is provided over a greaterlongitudinal and or transverse extent).

FIGS. 4A, 4B and 4C depict alternative electrode array 200, 400configurations suitable for being comprised in an implantable stimulator100, 101, 102 as described herein.

FIG. 4A depicts an implantable distal end of a further embodiment 103 ofa stimulator. Similar to the distal end depicted in FIG. 1C, the firstsurface 310 comprises:

-   -   two electrodes 200 a, 200 b of a first type and two electrodes        400 a, 400 b of a second type. From proximal to distal end, the        order depicted is 200 a, 400 a, 200 b, 400 b—in other words,        each electrode of the first type 200 a, 200 b is proximate an        electrode of the second type 400 a, 400 b and comprised in the        same surface 310.

The distal end depicted in FIG. 4A is the same as that depicted in FIG.1A, except:

-   -   the electrodes 200, 400 are extended at angle to the        longitudinal axis 600. This may reduce the sensitivity to        longitudinal misalignment because the longitudinal locations        over which tissue stimulation may be provided are increased.

Additionally or alternatively, the second surface 320 may similarlycomprise two electrodes 200 a, 200 b of the first type and twoelectrodes 400 a, 400 b of the second type.

As discussed above, each electrode 200 a, 200 b, 400 a, 400 b may beoperated as one or more stimulation electrodes or operated as one ormore return electrodes.

FIG. 4B depicts an implantable distal end of a further embodiment 104 ofa stimulator. Similar to the distal end depicted in FIG. 1C, the firstsurface 310 comprises four electrodes. However, in this embodiment 104,the first surface 310 comprises:

-   -   four electrodes 200 a, 200 b, 200 c, 200 d of a first type and        an electrode 400 of a second type. From proximal to distal end,        the order depicted is 200 a, 200 b, 200 c, 200 d. Transversely        adjacent to the four electrodes of the first type 200 is an        electrode of the second type 400, extending longitudinally to be        adjacent to each electrode of the first type 200.

Nominally, the electrodes of the first type 200 may be operated as oneor more stimulation electrodes. The electrode of the second type 400 maybe nominally operated as a return electrode for one or more of thestimulation electrodes.

This may reduce the sensitivity to longitudinal misalignment because thefour different longitudinal locations are provided which may be selectedfor stimulation over which tissue stimulation may be provided areincreased.

Additionally or alternatively, the second surface 320 may similarlycomprise four electrodes 200 a, 200 b, 200 c, 2003 of the first type andone adjacent and longitudinally extended electrode 400 of the secondtype.

As discussed above, each electrode 200 a, 200 b, 200 c, 200 d, 400 maybe operated as one or more stimulation electrodes or operated as one ormore return electrodes.

FIG. 4C depicts an implantable distal end of a further embodiment 105 ofa stimulator. Similar to the distal end depicted in FIG. 4B, the firstsurface 310 comprises four electrodes 200 a, 200 b, 200 c, 200 d of afirst type. However, in this embodiment 105, the first surface 310further comprises four adjacent electrodes 400 a, 400 b, 400 c, 400 d ofa second type. From proximal to distal end, the order depicted is 200a/400 a, 200 b/400 b, 200 c/400 c, 200 d/400 d. Transversely adjacent toeach of the four electrodes of the first type 200 is an electrode of thesecond type 400 at approximately the same disposition along thelongitudinal axis 600.

Nominally, the electrodes of the first type 200 may be operated as oneor more stimulation electrodes. The electrodes of the second type 400may be nominally operated as a return electrode for one or more of thestimulation electrodes. Nominally, adjacent electrodes may be consideredas a stimulation/return pair 200/400.

In other words, a 2×4 electrode array is provided—two along a transverseaxis and four along the longitudinal axis.

This may reduce the sensitivity to longitudinal misalignment because thefour different stimulation/return 200/400 pairs are provided atsubstantially different longitudinal locations are provided which may beselected for stimulation over which tissue stimulation may be providedare increased.

Additionally or alternatively, the second surface 320 may similarlycomprise four electrodes 200 a, 200 b, 200 c, 200 d of the first typeand four adjacent electrodes 400 a, 400 b, 400 c, 400 d of the secondtype.

As discussed above, each electrode 200 a, 200 b, 200 c, 200 d, 400 a,400 b, 400 c, 400 d may be operated as one or more stimulationelectrodes or operated as one or more return electrodes. This may alsoreduce the sensitivity to a transverse misalignment.

The stimulator 100, 101, 102, 103, 104, 105 may further comprise:

-   -   an energy receiver, configured and arranged to wirelessly        receive energy from an associated energy transmitter when the        associated energy transmitter is proximate;

the pulse generator 500 being further configured and arranged to receiveelectrical energy from the energy receiver for its operation.

FIG. 5 and FIG. 6 depict configurations of nerves that may be stimulatedusing a suitably configured implantable distal end of stimulators 100,101, 102, 103, 104, 105 to provide neurostimulation to treat conditionssuch as headaches or primary headaches.

FIG. 5 depicts the left supraorbital nerve 910 and right supraorbitalnerve 920 which may be electrically stimulated using a suitablyconfigured device. FIG. 6 depicts the left greater occipital nerve 930and right greater occipital nerve 940 which may also be electricallystimulated using a suitably configured device.

Depending on the size of the region to be stimulated and the dimensionsof the part of the device to be implanted, a suitable location isdetermined to provide the electrical stimulation required for thetreatment. Approximate implant locations for the distal part of thestimulation device comprising stimulation devices 100, 101, 102, 103,104, 105 are depicted as regions:

-   -   location 810 for left supraorbital stimulation and location 820        for right supraorbital stimulation for treating chronic headache        such as migraine and cluster.    -   location 830 for left occipital stimulation and location 840 for        right occipital stimulation for treating chronic headache such        as migraine, cluster, and occipital neuralgia.

In many cases, these will be the approximate locations 810, 820, 830,840 for the implantable stimulator 100, 101, 102, 103, 104, 105.

For each implant location, 810, 820, 830, 840 a separate stimulationsystem may be used. Where implant locations 810, 820, 830, 840 are closetogether, or even overlapping, a single stimulation system may beconfigured to stimulate at more than one implant location 810, 820, 830,840.

A plurality of stimulation devices 100, 101, 102, 103, 104, 105 may beoperated separately, simultaneously, sequentially or any combinationthereof to provide the required treatment.

FIG. 7 depict further configurations of nerves that may be stimulatedusing a suitably configured improved implantable stimulator 100, 101,102, 103, 104, 105 to provide neurostimulation to treat otherconditions. The locations depicted in FIG. 5 and FIG. 6 (810, 820, 830,840) are also depicted in FIG. 7.

Depending on the size of the region to be stimulated and the dimensionsof the part of the device to be implanted, a suitable location isdetermined to provide the electrical stimulation required for thetreatment. Approximate implant locations for the part of the stimulationdevice comprising stimulation electrodes are depicted as regions:

-   -   location 810 for cortical stimulation for treating epilepsy;    -   location 850 for deep brain stimulation for tremor control        treatment in Parkinson's disease patients; treating dystonia,        obesity, essential tremor, depression, epilepsy, obsessive        compulsive disorder, Alzheimer's, anxiety, bulimia, tinnitus,        traumatic brain injury, Tourette's, sleep disorders, autism,        bipolar; and stroke recovery    -   location 860 for vagus nerve stimulation for treating epilepsy,        depression, anxiety, bulimia, obesity, tinnitus, obsessive        compulsive disorder, heart failure, Crohn's disease and        rheumatoid arthritis;    -   location 860 for carotid artery or carotid sinus stimulation for        treating hypertension;    -   location 860 for hypoglossal & phrenic nerve stimulation for        treating sleep apnea;    -   location 865 for cerebral spinal cord stimulation for treating        chronic neck pain;    -   location 870 for peripheral nerve stimulation for treating limb        pain, migraines, extremity pain;    -   location 875 for spinal cord stimulation for treating chronic        lower back pain, angina, asthma, pain in general;    -   location 880 for gastric stimulation for treatment of obesity,        bulimia, interstitial cystitis;    -   location 885 for sacral & pudendal nerve stimulation for        treatment of interstitial cystitis;    -   location 885 for sacral nerve stimulation for treatment of        urinary incontinence, fecal incontinence;    -   location 890 for sacral neuromodulation for bladder control        treatment; and    -   location 895 for fibular nerve stimulation for treating gait or        footdrop.

Other conditions that may be treated include gastro-esophageal refluxdisease, an autoimmune disorder, inflammatory bowel disease andinflammatory diseases.

The conformability and minimum thickness of the substrate 100 andelectrode array 200, 400 makes one or more implantable stimulators 100,101, 102, 103, 104, 105 highly advantageous for the stimulation of oneor more nerves, one or more muscles, one or more organs, spinal cordtissue, brain tissue, one or more cortical surface regions, one or moresulci, and any combination thereof.

The descriptions thereof herein should not be understood to prescribe afixed order of performing the method steps described therein. Rather themethod steps may be performed in any order that is practicable.Similarly, the examples used to explain the algorithm are presented asnon-limiting examples, and are not intended to represent the onlyimplementations of these algorithms. The person skilled in the art willbe able to conceive many different ways to achieve the samefunctionality as provided by the embodiments described herein.

Many types of implantable distal ends of stimulation devices aredepicted. But this does not exclude that the rest of the device isimplanted. This should be interpreted as meaning that at least theelectrode section of the distal end is preferably configured andarranged to be implanted.

Although the present invention has been described in connection withspecific exemplary embodiments, it should be understood that variouschanges, substitutions, and alterations apparent to those skilled in theart can be made to the disclosed embodiments without departing from thespirit and scope of the invention as set forth in the appended claims.

In a non-limiting example,

-   -   one or more electrodes of the first type 200 a, 200 b are        comprised in the first surface 310 and one or more electrodes of        the second type 400 a, 400 b are comprised in the second surface        320; or    -   one or more electrodes of the first type 200 a, 200 b are        comprised in the first surface 310 and one or more electrodes of        the second type 400 a, 400 b are also comprised in the first        surface 310; or    -   one or more electrodes of the first type 200 a, 200 b are        comprised in the second surface 320 and one or more electrodes        of the second type 400 a, 400 b are comprised in the first        surface 310; or    -   one or more electrodes of the first type 200 a, 200 b are        comprised in the second surface 320 and one or more electrodes        of the second type 400 a, 400 b are also comprised in the second        surface 320; or    -   any combination thereof.

The stimulator 100, 101, 102, 103, 104, 105 may be further modified. Ina non-limiting example:

-   -   the foil-like substrate 300 and pulse generator 500 may be        embedded in one or more flexible bio-compatible encapsulation        layers. These layers may comprise: a Liquid Crystal Polymer        (LCP), a Polydimethylsiloxane (PDMS), a silicone polyurethane, a        Polyimide, a parylene, a biocompatible polymer, a biocompatible        elastomer, and any combination thereof.

By providing relatively larger higher electrode 200, 400 surfaces,stimulators 100, 101, 102, 103, 104, 105 may be operated at a lowerenergy/lower power. This may be advantageous in applications where highfrequency and/or burst stimulation is used.

High frequency operation may require more energy to be provided by thepulse generator 500. In applications where energy/power is critical,such as, in a non-limiting example, if an increased operating lifetimeis desired from a power source for the pulse generator 500, anyreduction in required power may be advantageous. High frequencyoperation may be considered as generating electrical stimulation pulseswith a frequency of 1000 Hz or more, preferably 1500 Hz or more, morepreferably 2000 Hz or more, yet more preferably 2500 Hz or more.

In an embodiment, experiments with burst stimulation have been performedsuch as Burst Occipital Nerve Stimulation for Chronic Migraine andChronic Cluster Headache by Garcia-Ortega et al, Neuromodulation 2019;22: 638-644, DOI: 10.1111/ner.12977.

For burst operation, the pulse generator 500 is further configured andarranged to generate electrical stimulation pulses in groups ofstimulation pulses.

In a non-limiting example, groups (or bursts) of stimulation pulses maycomprise 2 to 10 pulses, more preferably 2 to 5 stimulation pulses.Stimulation pulses in a group may have a repetition frequency of morethan 500 Hz, typically 1000 Hz or more.

Groups may be repeated at more than 5 Hz, typically 40 Hz or more.

As with high frequency operations, burst operation may require moreenergy to be provided by the pulse generator 500, and any reduction inrequired power may be advantageous.

Additionally, the speed of charge-balance recovery may also increasewith a lower impedance. By using a relatively thin-foil substrate 300,stimulation between an electrode of the first type 200 comprised in onesurface 310, 320 and an electrode of the second type 400 comprised inthe other surface 310, 320, the current path in tissue is relativelyshort, reducing impedance.

Similarly, using a substrate 300, and stimulation between an electrodeof the first type 200 comprised in one surface 310, 320 and an adjacentelectrode of the second type 400 comprised in the same surface 310, 320,provide a relatively short path through tissue.

While certain illustrative embodiments have been described, it isevident that many alternatives, modifications, permutations andvariations will become apparent to those skilled in the art in light ofthe foregoing description.

What is claimed is:
 1. An implantable stimulator comprising: a pulsegenerator for generating one or more electrical treatment stimulationpulses; a conformable foil-like substrate, having a longitudinal axisextending from the pulse generator to a distal end of the substrate, thesubstrate comprising one or more adjacent polymeric substrate layers,the substrate having a first and second planar surface; an electrodearray, proximate the distal end, having a first and second electrodecomprised in the first or second surface, each electrode in operationbeing configurable for transferring treatment energy to and/or fromhuman or animal tissue; the implantable stimulator further comprising:one or more electrical interconnections, between the pulse generator andthe first and the second electrodes, for transferring electrical energyas one or more electrical treatment stimulation pulses to the firstelectrode and/or the second electrodes; where the one or more electricalinterconnections are comprised between the first and second surfaces,and the conformable foil-like substrate has a maximum thickness of 0.5millimeter or less, proximate the first and second electrodes, thethickness being determined by a perpendicular distance betweencorresponding points on the first and second outer planar surfaces. 2.The stimulator according to claim 1, where the maximum thickness of thesubstrate proximate the first and second electrodes is 0.3 millimetersor less, even more preferably 0.2 millimeters or less, yet morepreferably 0.1 millimeters or less.
 3. The stimulator according to claim1, where the maximum thickness of the implantable stimulator proximatethe pulse generator is 5 millimeters or less, preferably 4 millimetersor less, even more preferably 3 millimeters or less, the thickness beingdetermined by a perpendicular distance between corresponding points onouter planar surfaces.
 4. The stimulator according to claim 1, where:the substrate has a surface comprised in a plane with a transverseextent substantially perpendicular to the longitudinal axis; where thedistal end of the substrate has a maximum planar width, the width beingdetermined by a perpendicular distance between corresponding points onouter surfaces edges of the substrate along the transverse extent; andwhere the ratio of maximum planar width to maximum thickness proximatethe first and second electrodes being 7:1 or higher, preferably 10:1 orhigher, more preferably 15:1 or higher, yet more preferably 30:1 orhigher, even more preferably 50:1 or higher.
 5. The stimulator accordingto claim 1, where the pulse generator is further configured to operatein: a first electrode mode, where electrical stimulation energy isprovided to the first electrode as one or more electrical treatmentstimulation pulses, the second electrode being configured to provide, inuse, a corresponding electrical return for the first electrode; or asecond electrode mode, wherein electrical stimulation energy is providedto the second electrode as one or more electrical treatment stimulationpulses, the first electrode being configured to provide a correspondingelectrical return for the second electrode during operation; thestimulator being further configured and arranged to switch the pulsegenerator under predetermined and/or controlled conditions between thefirst and second electrode modes.
 6. The stimulator according to claim1, where: the first electrode is comprised in the first surface and thesecond electrode is comprised in the second surface; and/or the firstelectrode is comprised in the first surface and the second electrode iscomprised in the first surface; and/or the first electrode is comprisedin the second surface and the second electrode is comprised in the firstsurface; and/or the first electrode is comprised in the second surfaceand the second electrode is comprised in the second surface; and/or anycombination thereof.
 7. The stimulator according to claim 1, wherein twoor more electrodes are configurable using one or more parameters of thepulse generator as a stimulation electrode or a return electrode.
 8. Thestimulator according to claim 1, where the stimulator further comprises:an energy receiver, configured and arranged to wirelessly receive energyfrom an associated energy transmitter when the associated energytransmitter is proximate; the pulse generator being further configuredand arranged to receive electrical energy from the energy receiver forits operation.
 9. The stimulator according to claim 1, where thesubstrate comprises one or more layers of a Liquid Crystal Polymer (LCP)film.
 10. The stimulator according to claim 1, where the pulse generatoris comprised between the first and second planar surfaces.
 11. Thestimulator according to claim 1, where the substrate and pulse generatorare embedded in one or more flexible bio-compatible encapsulationlayers.
 12. The stimulator according to claim 11, where the one or moreencapsulation layers further comprise a Liquid Crystal Polymer (LCP), aPolydimethylsiloxane (PDMS), a silicone polyurethane, a Polyimide, aparylene, a biocompatible polymer, a biocompatible elastomer, and anycombination thereof.
 13. The stimulator according to claim 1, where thepulse generator is further configured and arranged to generateelectrical stimulation pulses with a frequency of 1000 Hz or more,preferably 1500 Hz or more, more preferably 2000 Hz or more, yet morepreferably 2500 Hz or more.
 14. The stimulator according to claim 1,where the pulse generator is further configured and arranged to generateelectrical stimulation pulses in groups of stimulation pulses.
 15. Thestimulator according to claim 14, where the groups of stimulation pulsescomprise 2 to 10 pulses, more preferably 2 to 5 stimulation pulses. 16.The stimulator according to claim 1, where the one or more electricalinterconnections are comprised in one or more conductive interconnectionlayers, the one or more conductive interconnection layers beingcomprised between two adjacent polymeric substrate layers.
 17. Thestimulator according to claim 1 when in operation stimulating one ormore nerves, one or more muscles, one or more organs, spinal cordtissue, brain tissue, one or more cortical surface regions, one or moresulci, and any combination thereof.
 18. The stimulator according toclaim 1 operational to treat headaches, primary headaches, incontinence,occipital neuralgia, sleep apnea, hypertension, gastro-esophageal refluxdisease, an inflammatory disease, limb pain, leg pain, back pain, lowerback pain, phantom pain, chronic pain, epilepsy, an overactive bladder,poststroke pain, obesity, an autoimmune disorder, rheumatoid arthritis,inflammatory bowel disease, Crohn's disease, and any combinationthereof.